The order issued yesterday by John Kelly doesn’t say that rocks will be treated like bullets. In fact, the “use of force” element may be the least controversial part of it. Of course the military can use force — proportionately, to defend themselves if force is used against them first. What’s more interesting are the details about crowd control and detaining people, tasks that the military normally isn’t allowed to do per the Posse Comitatus Act.

The new “Cabinet order” was signed by White House Chief of Staff John Kelly, not President Donald Trump. It allows “Department of Defense military personnel” to “perform those military protective activities that the Secretary of Defense determines are reasonably necessary” to protect border agents, including “a show or use of force (including lethal force, where necessary), crowd control, temporary detention. and cursory search.”…

The Congressional Research Service, the non-partisan research agency for Congress, has found that “case law indicates that ‘execution of the law’ in violation of the Posse Comitatus Act occurs (a) when the Armed Forces perform tasks assigned to an organ of civil government, or (b) when the Armed Forces perform tasks assigned to them solely for purposes of civilian government.” However, the law also allows the president “to use military force to suppress insurrection or to enforce federal authority,” CRS has found.

Kelly said in the signed directive that the additional authorities were necessary because “credible evidence and intelligence” have indicated that the thousands of migrants who have now made their way to the U.S. checkpoint near Tijuana, Mexico, “may prompt incidents of violence and disorder” that could threaten border officials.

Is the White House treating immigration at the border as an “insurrection”? (Can foreigners even be guilty of an insurrection?) The Insurrection Act says that “Whenever there is an insurrection in any State against its government, the President may, upon the request of its legislature or of its governor if the legislature cannot be convened, call into Federal service such of the militia of the other States, in the number requested by that State, and use such of the armed forces, as he considers necessary to suppress the insurrection.” A similar statute lets him call in the military when “unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings.” How to harmonize those laws with the Posse Comitatus Act, which forbids the military from performing U.S. law enforcement duties, is for the lawyers to hash out. Given the judiciary’s hostility to Trump’s more novel policy moves, I wouldn’t bet on any arrests at the border made by American troops holding up in court on “insurrection” grounds.

But they won’t be making arrests. The man empowered by Kelly’s order to set the rules of engagement here is James Mattis, and Mattis is much less inclined to ignore norms of government than his boss is. Trump doesn’t call him “Moderate Dog Mattis” for nothing.

We are at nearly 40 mins with #SecDef in press gaggle – lots more on borderto come. Bottom line from Secretary Mattis – US forces will NOT act in violation of Posse Comitatus pic.twitter.com/vIHxTHYLDj

SecDef Mattis On detention: "I would put it in terms of minutes…if someone’s beating on a border patrolman and if we were in a position to have to have to do something about it we could stop them from beating on them and take them over and deliver them to a border patrolman" https://t.co/SevxqQx8af

Mattis also understands far better than Trump that American troops aren’t trained to perform law enforcement duties:

A politically conservative veteran’s reaction: “Using the military like this is an awful precedent and puts the soldiers down there in a no-win situation. It isn’t something a commander in chief who understands or respects the military would ever do.” https://t.co/1rUrEPtr0x

The SecDef has been embarrassed once over the border deployment, when he insisted that the U.S. military doesn’t do “stunts” only to have the midterm-focused timing of the mission cited repeatedly by critics in characterizing it that way. (If it’s a stunt, it’s an expensive one.) Some troops stationed at the border are already preparing to return home even though the caravan hasn’t arrived yet. Mattis isn’t going to compound the headache by mainstreaming the practice of using American soldiers as an auxiliary Border Patrol via ordering them to start carrying out basic BP functions. And no doubt John Kelly knows it.

Which brings us to the most interesting detail in the story: Why did Kelly, not Trump, issue the “cabinet order” here? Some on Twitter speculated this morning that maybe they did it that way to try to insulate Trump from the consequences in case things get hairy between the troops and the caravan once the two sides finally come face to face. I don’t think that’s it, though. Trump is already on record per the clip up above about wanting the military to shoot if any rocks are thrown at them. He’s not afraid of being blamed for a confrontation; if anything, he probably thinks a melee would be a useful deterrent to other would-be illegals by showing them what awaits if they try to sneak into the U.S. The fact that Kelly signed the order rather than Trump might even give illegals who are detained by the military a defense in court, that they were arrested pursuant to authority that was never formally granted by the commander-in-chief.

The reason Kelly’s name is on the order, I’m thinking, is that it was his idea. And maybe the reason it was his idea is because both his job and especially that of his protege, Kirstjen Nielsen, are hanging by a thread. Nielsen in particular is reportedly all but gone due to Trump’s dissatisfaction with the pace of illegal immigration on her watch. Maybe this order was Kelly’s way of placating POTUS. In return for Trump leaving Nielsen in place for now, Kelly would lend his own name and authority as a former four-star Marine to the idea of expanding the troops’ powers to fight illegal immigration — knowing full well that Mattis would instruct underlings not to exploit that grant of power. (Which wouldn’t be the first time Mattis and Kelly had quietly teamed up to restrain Trump.) A showy order to the Pentagon about taking the gloves off on the border that won’t amount to much of anything in practice might please Trump and thus protect Kelly and Nielsen. For awhile. Exit quotation from Mattis: “We are not doing law enforcement. We do not have arrest authority.”